1. Field of the Invention
The present invention relates to a vapor phase synthesis of hexafluoroisobutylene directly from hexafluoropropylene oxide. The present invention also relates to a vapor phase synthesis of hexafluoroisobutylene directly from hexafluoropropene.
2. Description of the Prior Art
Hexafluoroisobutylene is a known compound which is known to be useful for a variety of purposes such as, for example, a comonomer which forms polymers of exceptional thermal, chemical and mechanical properties with other comonomers such as vinylidene fluoride. The preparation of such copolymers is described in U.S. Pat. No. 3,706,723 to Chandrasekeran et al., issued Dec. 19, 1972.
Hexafluoroisobutylene has been previously prepared by methods which include the reaction of hexafluoroacetone with ketene (U.S. Pat. No. 3,894,097 to N. Vanderkooi), the reaction of hexafluorothioacetone with ketene or a ketene-generating compound (U.S. Pat. No. 4,244,891 to Van Der Puy et al.), the reaction of antimony trifluorodichloride with a chlorofluoroisobutylene [R. N. Hazeldine, J. Chem. Soc., 3565 (1953)]and the dehydration of hexafluoro-2-methyl-2-propanol with phosphorus pentachlordie [M. H. Kaufman et al., J. Org. Chem. 31, 3090 (1966)]or with sulfur tetrafluoride (E. E. Gilbert et al. in U.S. Pat. No. 3,656,786). See also U.S. Pat. No. 4,367,394 (Anello) which discloses a liquid phase synthesis of hexafluoroisobutylene starting from hexafluoropropene, elemental sulfur, and alkali metal fluoride in an aprotic solvent.
U.S. Pat. No. 4,165,340 (Tohzuka et al.) discloses a process for preparing hexafluoropropanone-2 from hexafluropropene by one step reaction which comprises contacting hexafluoropropene and oxygen with a fluorinated alumina or a fluorinated silica-alumina as a catalyst in the presence or absence of water, provided that water is present when the catalyst is the fluorinated alumina. See also U.S. Pat. Nos. 4,284,822 and 4,057,584 also to Tohzuka et al.
U.S. Pat. No. 3,600,409 (Milian et al.) discloses a process for oxidation of hexafluoropropene to hexafluoropropylene epoxide, which operates in the presence of an inert aromatic compound to eliminate the formation of hexafluoroacetone.
These preparations and others suffer trom one or more disadvantages from a commercial standpoint. For example, although the preparation involving hexafluoroacetone is a high-yield process, hexafluoroacetone represents a starting material of high cost, high toxicity and limited availability. The chlorofluoroisobutylene route involves several steps including a slow dehydrochlorination step, while the dehydration of the fluorinated tertiary butyl alcohol requires excessively long reaction times or expensive reagents The reaction of hexafluorothioacetone with ketene operates in the gas phase at elevated temperature (300.degree.-800.degree. C.) and requires special precautions for handling and preparing hexafluorothioacetone.
It is accordingly an object of the invention to provide a new one stage route to hexafluoroisobutylene which utilizes cheaper and more readily accessible starting materials and which operates without isolation of toxic intermediates.
Other objects and advantages of the invention will become apparent from the following description.